Band element for pneumatic tire and method of making same

ABSTRACT

A band element for mounting in the crown portion of a pneumatic tire to provide run flat ability to the tire in the event of loss of air pressure and to provide increased puncture resistance. The band is formed of flat strips of tape having fibers embedded in a resin matrix which are twisted and then pultrated to provide a rectangular cross sectional configuration. The twisted tape is wrapped about a mandrel and forms either the only layer, or the intermediate layer of a composite band in combination with inner and outer layers of flat tape or wound filament fibers, whereby the fibers in the tape extend across the central axis of the band to reduce interlaminar sheer. In another embodiment, a plurality of dimples or depressions are formed in the individual tape layers to extend a plurality of the fibers across the layer boundaries to reduce interlaminar sheer.

CROSS REFERENCE TO RELATED APPLICATION

This application is a division of application Ser. No. 09/120,210, filedJul. 21, 1998.

BACKGROUND OF THE INVENTION

1. Technical Field

The invention relates to reinforced resilient pneumatic tires and moreparticularly to a vehicle tire reinforced by a thin annular compositeband which enables the tire to run in an unpressurized condition and toprovide greater puncture resistance for the tire. More particularly, theinvention relates to a pneumatic tire in which the band element isformed of twisted material strips having fibers which are orientedwithin the band to extend across the neutral axis of the band and notfall within the axial plane of the neutral axis to provide the band withenhanced ability to resist interlaminar shear stresses and provideenhanced inflated and uninflated banded tire durability and punctureresistance.

2. Background Information

Various tire constructions have been devised over the years which enablea tire to run in an under-inflated or non-inflated condition, such asafter receiving a puncture and loss of pressurized air, for extendedperiods of time and at relatively high speeds. This enables the vehicleoperator to safely drive the vehicle to an appropriate location forrepair or replacement of the punctured tire. Certain of these safetytires, referred to as “run flat tires”, have been successful for certainapplications and certain types of tire constructions. Most of these runflat tires achieve their run flat capability, by the placement ofreinforcing layers or members of relatively stiff elastomeric materialin the side walls of the tire which enable the tire to support thevehicle weight even with the complete loss of internal air pressure.Examples of such prior art run flat tire constructions which use suchsidewall inserts are shown in U.S. Pat. Nos. 3,911,987; 3,949,798;3,954,131; 4,067,372; 4,202,393; 4,203,481; 4,261,405; 4,265,288;4,287,924; 4,365,659; 4,917,164; and 4,929,684.

In addition to these prior art run flat tires, various run flat tireconstructions have been developed which utilize a thin annular bandwhich extends circumferentially throughout the tire beneath the treadarea. Examples of such banded run flat tires are shown in the followingpatents.

U. S. Pat. No. 4,428,411 describes a method to make a particular bandfor use in a run flat tire which uses a series of side-by-side elementsin the form a helix. The band has hoop compression as against aconventional breaker belt that has no significant compressive strengthbut is used only to resist tension loads endured by the tire whenpressurized.

U.S. Pat. Nos. 4,673,014 and 4,794,966 teach a method to acquiredesirable prestressing in a fabricated band made of helical elements.Physically bending the larger diameter helix element around a smallermandrel and securing it with a resin impregnated tape acquires adesirable level of prestressing.

U.S. Pat. No. 4,456,048 teaches a method of acquiring a change in bandstiffness as a function of deflection. The band has a lower stiffnessfor normal pressurized operation and has a higher stiffness to supportload when the tire is uninflated and experiences larger deflection.

Japanese Patent application No. JP 63141809 discloses a run flat tirehaving a banded element which is formed of layered strips of materials,such as an arramed filament which is impregnated with a high elasticityepoxy resin, which after hardening provides a stiffened band. The tireof this disclosure requires that elastomeric side wall inserts beutilized in combination with the band in order to achieve the desiredrun flat characteristics.

Other run flat banded pneumatic tires are shown in U.S. Pat. Nos.4,111,249; 4,318,434; 4,428,411; 4,459,167; and 4,734,144.

Banded tires have been fabricated with band materials made of steel,aluminum, titanium, and epoxy and thermoplastic composites with glass,KEVLAR (aromatic polyamide) and graphite fiber reinforcement. The commonfailure mode with such lightweight, economical laminate bandconstructions is interlaminar shear within the band's primary bendingneutral axis. This is a fatigue failure and is directly related to thespectrum of cyclic operating stress. As in all fatigue failures, thelower the stress, the longer the operating life. This problem of fatiguefailure occurring along the neutral axis of the band resulting ininterlaminar shear can be reduced by the prestressing the band duringits manufacture, as described in pending patent application Ser. No.08/782,364.

Numerous prior art pneumatic tires have been provided with an annularband usually of metal, to resist puncture by sharp objects protrudingthrough the tread area. Although these prior art puncture resistanttires utilizing a metal band provide the desired puncture resistance, inmost cases, the metal band effects the ride characteristic of the tireand the life expectancy thereof.

Thus, it is desirable to provide a band element for run flat pneumatictires and for pneumatic tires having greater puncture resistance, withincreased resistance to interlaminar shear stress in the inflateddeflected banded tire, the uninflated deflected banded tire and thecondition of a banded tire encountering a road surface anomaly, which isaccomplished without materially increasing the difficulty of themanufacturing process for producing the band element and withoutmaterially increasing the cost thereof. The band element of the presentinvention achieves these results.

SUMMARY OF THE INVENTION

Objectives of the invention include. providing an improved pneumatictire that is substantially similar in ride, comfort, durability andoperation as conventional pneumatic tires, yet which is able to beoperated safely at reasonable speeds and for a sufficient number ofmiles after loss of internal pressurization.

Another objective of the invention is providing such a pneumatic tireand band element therefor which has enhanced load carrying capability,improved endurance by minimizing band stress, and in particularminimizes interlaminar shear stresses heretofore resulting indestruction of the band element.

Still another objective is to provide such a band element for use in apneumatic tire in which the band element is formed of usual tape stripshaving longitudinally extending fibers embedded in a resin with the tapebeing arranged during the construction of the band so that a substantialportion of the fibers extend over the neutral axis of the band which isthe area most susceptible to interlaminar shear.

A still further objective of the invention is to provide such a bandelement for run flat tires in which the individual tape strips whichform the band have longitudinally extending fibers embedded within aresin, are twisted into a cylindrical configuration and then pultratedinto a rectangular configuration for subsequent wrapping about a mandrelinto an annular band having one or more inner and outer layers of theconventional flat tape strips extending about the intermediate pultratedstrip layers.

Another objective of the invention is to provide such a band elementwherein a plurality of the flat strips containing the longitudinallyextending fibers embedded in the resin matrix, are placed injuxtaposition prior to being twisted into a cylindrical configurationfor subsequent pultration into a rectangular configuration to provide astronger layer having the fibers extending across the neutral axis toincrease resistance to interlaminar shear.

A still further objective of the invention is to provide such a run flattire which has increased puncture resistance from the tread contactingroad hazards, which can be manufactured at a cost and weight competitivewith conventional non run flat tire constructions and which will permitthe elimination of a spare tire conventionally required in automobilesthereby providing a cost saving to vehicle manufacturers and owners.

These objectives and advantages are improved by the method of thepresent invention, the general nature of which may be stated asincluding a method of forming a thin annular band for embedding in acrown portion of a pneumatic tire including the steps of providing athin flat strip of material formed with a plurality of longitudinallyextending fibers embedded in a resin matrix; twisting the strip untilthe strip assumes a substantially circular cross section throughout itslength; pultrating the twisted strip through a die to provide the stripwith a substantially rectangular s cross section; and wrapping thepultrated: strip about a mandrel to form the band having a plurality ofadjacent convolutions of said pultrated twisted strip.

These objectives and advantages are further obtained by the improvedannular band of the present invention, the general nature of which maybe stated as a band for embedding in a crown portion of a pneumatictire, said band having an axial width and a radial thickness with aneutral axis extending generally through the center of the band in anaxial direction, said band further including at least one elongatedstrip of material having a plurality of longitudinally extending fibersembedded in a resin matrix; said strip being wound into an annular shapehaving a plurality of adjacent convolutions extending in the axialdirection across the band and forming the axial band width, with certainof the longitudinal fibers extending across the neutral axis of theband.

These objectives and advantages are further obtained by providing apneumatic tire, the general nature of which may be stated as includingan elastomeric casing with a tread formed in a crown portion thereof andsidewalls extending from the crown portion to generally circular beadsadapted to normally seat themselves in an airtight secured relationshipwith a wheel; a band member comprising a continuous thin annularcomposite band fixed in the crown portion of said tire radially inwardlyof said tread having an axial width and a radial thickness with aneutral axis extending generally through the center of the band in anaxial direction, said band being formed of at least one elongated stripof material having a plurality of longitudinally extending fibersembedded in a resin matrix wound into an annular shape and having aplurality of adjacent convolutions extending in the axial directionacross the band and forming the axis width with certain of thelongitudinal fibers extending across the neutral axis of the band. dr

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention, illustrative of the best modesin which applicants have contemplated applying the principles, are setforth in the following description and are shown in the drawings and areparticularly and distinctly pointed out and set forth in the appendedclaims.

FIG. 1 is a sectional view through a pneumatic tire having the improvedband element incorporated therein;

FIG. 2 is a diagrammatic side elevational view showing a run flat bandedtire in an inflated deflected position;

FIG. 3 is a greatly enlarged fragmentary diagrammatic view showing theforces exerted on a band element in the central footprint region of theinflated deflected banded tire of FIG. 2;

FIG. 4 is a fragmentary diagrammatic view of a multilayered tapecomposite band prior to deflection;

FIG. 5 is a greatly enlarged diagrammatic view showing the forcesexerted on the multilayered tape composite band element of FIG. 4 in thecentral footprint region of a tire;

FIG. 6 is a fragmentary diagrammatic view with a greatly enlarged endsection of a prior art multilayer tape composite band element with eachlayer being made up of a finite number of widths of tape placed in aside-by-side fashion;

FIG. 7 is a further enlarged view of the encircled portion of FIG. 6;

FIG. 8 is a very diagrammatic view of a conventional tape depicting thefibers extending longitudinally throughout the tape and contained in aresin;

FIG. 9 is a diagrammatic sequence of steps showing the conventionalcomposite tape of FIG. 8 being modified according to the presentinvention by applying a wrap or twist thereto;

FIG. 10 is a greatly enlarged diagrammatic transverse sectional view ofthe twisted tape of FIG. 9;

FIG. 11 is a greatly enlarged diagrammatic transverse sectional view ofthe twisted tape of FIG. 10 being pultruded through a rectangular die;

FIG. 12 is an enlarged diagrammatic side view of a compositemultilayered tape band element showing the twisted fibers in thepultruded tape of FIG. 11 extending across the neutral axis;

FIG. 12A is a diagrammatic perspective view showing the twistedpultrated tape strip of FIG. 11 being wound about a mandrel to form atleast one layer of a band element;

FIG. 13 is a view similar to FIG. 6 of a first embodiment of a bandelement of the present invention formed with the pultruded tape of FIG.11;

FIG. 14 is a further enlarged diagrammatic view of the encircled portionof FIG. 13;

FIG. 15 is a greatly enlarged diagrammatic sectional view of the bandelement of FIGS. 13 and 14 taken on line 15—15, FIG. 13;

FIG. 16 is a diagrammatic view similar to FIG. 9 showing the sequence oftwisting two adjacent tapes;

FIG. 17 is a diagrammatic end view of a band element similar to FIG. 13,formed with the double twisted tape of FIG. 16;

FIG. 18 is a greatly enlarged view of the encircled portion of FIG. 17;

FIG. 19 is a diagrammatic end view similar to FIGS. 13 and 17 of amodified band element in which inside and outside layers are placed in awrapped relationship with a central layer formed by placing the flattape of FIG. 8 at approximately 45 degrees relative to the band elementaxis;

FIG. 20 is a greatly enlarged view of the encircled portion of FIG. 19;

FIG. 21 is a greatly enlarged diagrammatic end view similar to FIGS. 13,17 and 19 showing a multilayer tape composite band element providingfibers that cross the neutral axis of the band element by havingimpressions made in the tape layers;

FIG. 22 is a greatly enlarged view of the encircled portion of FIG. 21;

FIG. 23 is a diagrammatic view similar to FIGS. 13, 17, 19 and 21 of aprior art band element formed of homogenous filaments wound in a uniformdistribution and embedded in a resin matrix;

FIG. 24 is a greatly enlarged view of the encircled portion of FIG. 23;

FIG. 25 is a view similar to FIGS. 13, 17, 19, 21 and 23 of anotherembodiment of a band element of the present invention in which thecentral portion of the band is formed with the pultruded twisted tape asshown in FIG. 11, and with the inner and outer layers being formed of auniform distribution of wound filament fibers such as shown in FIGS. 23and 24;

FIG. 26 is a further enlarged diagrammatic view of the encircled portionof FIG. 25;

FIG. 27 is another embodiment of a band element in which the band isformed as a single layer of the pultruded twisted tape as shown in FIG.11, without any inner and outer layers; and

FIG. 28 is a greatly enlarged view of the encircled portion of FIG. 27.

Similar numerals refer to similar parts throughout the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The improved pneumatic tire of the present invention containing theunique band element is indicated generally at 1 and is shown in crosssection in FIG. 1. Most of the components of tire 1 are of aconventional design and construction and consists generally of a pair ofbeads 2 which are adapted to be sealed in an air tight relationship on awheel. Tire 1 further comprises a carcass or casing 4 having an outerperipheral tread portion 5 formed in a crown region thereof, andsidewalls 7 extending on both sides from the crown portion to beads 2.Tread 5 is formed with a usual tread pattern depending upon theparticular characteristics to be achieved by the pneumatic tire and theparticular vehicle on which the tire will be mounted.

Sidewalls 7 of the casing are reinforced by usual radial reinforcingelements which extend throughout the sidewalls and are turned up aboutbeads 2. As is well known in the art, sidewall plies are reinforcedfibers composed of rayon, nylon, polyester, steel and other types ofknown materials. These sidewall reinforcements extend from at least thecrown portion of the tire and throughout the sidewalls to the bead areathereof.

In accordance with one of the main features of the invention, animproved annular stiffening band element indicated generally at 10, ismounted within the crown portion of the tire radially beneath the treadand extends circumferentially throughout the tire and extendinggenerally throughout the width of the tread. Band 10 is operativelyconnected to the sidewall reinforcing elements 8 either physically orthrough the intervening elastomeric material of the crown portion andtread which bonds the band to the reinforcing elements and radiallystabilizes the band. Band 10 is relatively thin in contrast to its widthand can range in width between 6 and 12 inches and in thicknessgenerally between 0.1 and 0.2 inches depending upon the particular tirein which it is bonded. It is also understood that tire 1 will have ausual innerliner, gum abrasive strips and other components present in aconventional pneumatic tire which are not shown in FIG. 1 or discussedin further detail.

As discussed above, one of the objects of the invention is the formationof band 10 so as to provide sufficient load carrying capability withimproved endurance by eliminating or materially reducing interlaminarshear by forming the band of material strips having fibers which areoriented within the band element to extend across the neutral axis ofthe band. The band behaves as a tension member when the tire ispressurized and acts as a structural compression member when the tire isin the unpressurized state which allows loads to act over a substantialportion of the circumference of the tire.

FIG. 2 shows tire 1 in an inflated deflected condition in which bandelement 10 in the central footprint region, flattens and conforms to theroad surface for a short distance on both sides of the center line 11 ofthe tire. Thus, in the central footprint region, the band elementgeometry has changed from being circular in the inflated undeflectedcondition to being flat in the inflated deflected position. Adiagrammatic enlargement of the band element in the central footprintregion is shown in FIG. 3. The change in band element axial geometryfrom circular to flat merely reflects the change in stress/strain regimewithin the band element caused by flattening of the band element.Consequently, in the central footprint region, the fibers along theinside diameter of the band element are in tension and elongate as shownby arrows 12 while the fibers along the outside diameter of the bandelement are in compression and are shortened as depicted by arrows 13.

In the uninflated deflected banded tire (not shown), the sidewallundergoes significantly more deflection vs. the inflated deflectedcondition shown in FIGS. 2 and 3. For this condition, the band elementand the central footprint region conforms to the road surface for alonger distance on either side of the center line of the tire vs. theinflated condition as shown in FIG. 2. An enlargement of a band elementformed of a multilayered tape composite in this uninflated deflectedcondition is shown in FIGS. 4 and 5 and is similar to that representedin FIG. 3 which represents a homogenous band. Here again, fibers 14 intape layers 15 along the inside diameter of the band are in tensionwhile fibers 16 in tape layers 17 along the outside diameter of the bandare in compression. Thus, although banded tire deflection is greateruninflated vs. inflated, the band element stress/strain regime in thecentral footprint region is basically the same for both conditions.

Although the critical design stress in the outer fibers of the bandelement occurs in the central footprint region, an additional cyclicstress exists forward and behind the footprint region in a general areaindicated by numeral 19 in FIG. 2, wherein the outer fibers of the bandelement are in maximum tension, approximately 45° ahead of and 45°behind center line 11 of the footprint. This condition increases withdeflection and accounts for the lower band element fatigue life for theuninflated condition vs. the inflated operation. The fatigue spectrumfor the band element fibers on the outside diameter is a combination ofthe dominant road contact (compression) plus two additional cycles oflower stress (tension). Similarly, the fatigue spectrum for band fiberson the inside diameter is a combination of the dominant road contact(tension) plus two additional cycles of lower stress (compression).

It is also a fact that when band 10 flattens in the central footprintregion, there is a natural shearing affect within the band element. Thiscondition must exist in order for the inside diameter band fibers 14 toelongate while the outside band fibers 16 are shortened. This internalband element shearing described as transverse shear, is shown in FIG. 5and is present to some degree regardless of band construction. FIGS. 4and 5 depicts a multilayer tape composite band element composed of amultitude of layers of fiber resin tapes indicated at 15 and 17, whichare wound in a plurality of layers. In this case, the transverse shearstress between the multilayer fiber/resin layers or tapes is calledinterlaminar shear stress. As shown in FIG. 5, the tension andcompression forces imposed on the band element upon flattening in thecentral footprint region induces identical levels of transverse shearstress. Thus, regardless of whether the band element is made ofhomogenous filament wound material or a multilayer tape/fiber resincomposite, the strain/stress regime and transverse shear develops tosome degree upon flattening of the band element in the central footprintregion because the outer fiber (inside diameter and outside diameter)stresses are proportional to the strains.

The magnitude of the interlaminar shear stress which initially developsalong the neutral axis 20 of the band, is dependent upon the tension andcompression stresses indicated in the outer fibers of the band element.The outer fiber tension and compression stresses are in turn dependenton the strains induced by flattening of the band element. The strain inthe outer fibers of the band element in the central footprint region canbe approximated by the following equation: ε=t/D.

Assuming the band element begins circular and is deflected flat in thecentral footprint region, the magnitude of the tension and compressionstresses in the outer fibers of the band element in this region aredependent upon the following: Radius (of diameter “D”) of theundeflected band element in the axial direction. Radial thickness “t” ofthe band element.

The radius of the band element is largely determined by the tire sizeand thus can be changed only within narrow limits. The band elementradial thickness will be determined so as to give acceptable bandelement outer fiber endurance as experienced by those fibers alternatingbetween tension and compression.

Banded tire durability, including both inflated and uninflatedconditions, is limited by the interlaminar shear strength of the bandelement. More specifically, band element durability, limited by failuredue to interlaminar shear, initiates near the axial ends 21 (FIG. 1) ofthe band element along neutral axis 20 and progresses toward the axialcenter 22 of the band element. This characterization of durabilityfailure within the band element is typical for both filament wound andmultilayer tape, tape composite band element constructions. However, inthe case of the multilayer tape composite band element, it is necessaryto distinguish between interlaminar shear stress failure within theindividual layers of the band element or interlaminar shear stressfailure at an interface between layers of the multilayer tape compositeband element. Generally, interlaminar shear strength is greater withinthe individual layers vs. between the layers. Nevertheless, in eachcase, the interlaminar shear failure is the result of the resin failingin shear. That is, the fibers within the fiber/resin composite do notfail. Rather, it is the shear strength of the resin which largelydetermines the strength of the band element within each layer or betweenthe layers. In all these cases, it would be advantageous to increase theresistance to interlaminar shear stress of the band element and therebyimprove band element durability by more effectively utilizing thestrength of the fibers within the composite band element.

Prior art techniques to improve band element durability have beenexplored. For example, an epoxy fiber filled coating on the edges of theband or an epoxy laminated glass fiber tape bonded to the axial ends ofthe band element have shown positive results. For multilayer tapecomposite band elements, efforts to improve shear strength betweencomposite layers include increasing the percentage of resin toreinforcing fiber around the neutral axis for thermoplastic composites.For thermoset composites, an increase in elastomeric additives withinthe epoxy around the same neutral axis area can provide an increase inshear strength between layers of the multilayer tape composite bandelement.

It is the purpose of this invention to increase interlaminar shearstrength not only near the axial ends 21 of the band element but alsoacross the entire axial length of the band element and thereby improveband element durability by fabricating the composite band element insuch a manner that fibers run across the neutral axis.

FIG. 6 is a diagrammatic sectional view of a prior art multilayer tapecomposite band element. In a micro sense, this band element 24 consistsof a finite number of layers, with each layer being made up of a finitenumber of widths or tapes 25 placed in side-by-side fashion, and witheach tape being made of a combination of many fibers embedded in asuitable resin or matrix. Also, within each layer, all the tapes willhave a certain angle of orientation. In the fabrication of themultilayer tape composite band element 24, tapes 25 in each layer may beplaced on a cylindrical surface or mandrel perpendicular to the bandelement axis, or with an angular orientation relative to the normal ofthe band element axis as shown in pending patent application Ser. No.08/782,364, the contents of which are incorporated herein by reference,in a heated state and wrapped under pressure. The essence of thisinvention is. not the number or angular orientation of these layers, butthe fiber orientation locally within the individual tapes and globallywithin the layers.

Fiber orientation is better understood by referring to FIG. 8, whichdepicts a conventional tape 26 prior to being placed upon the buildingmandrel. Tape 26 has a pair of opposed flat side surfaces 28 a and 28 band opposed longitudinal edges 28 c and 28 d. The composite tapeconsists of a resin 27 or matrix which binds numerous fibers 28 togetherand which, as a thermoplastic aggregate, can be handled as necessaryduring the fabrication process. The orientation of the numerous fibers28 within this tape are basically aligned longitudinally with the lengthof the tape.

In the fabrication of conventional tapes 26 as just described, thefibers 28 are oriented longitudinally owing to the pultrusion process ofresin/fiber preparation. In light of this, it is not likely to arrangethe fibers in any way but longitudinally. Thus, in order to improveinterlaminar shear strength, either within layers or between layers of amultilayer tape composite band element using conventional tapes, clearlyan alternative approach is needed.

This alternative approach begins with a conventional thermoplasticcomposite tape 26 which is subsequently modified by applying a wrap ortwist per unit length as shown in FIG. 9. Tape 26 is twisted until thesuccessive turns close in on each other such that the twisted tape 30assumes a circular cross section throughout its entire length, as shownin FIG. 10. This twisted tape 30 then is pultrated through a square orrectangular die 31 as shown in FIG. 11, where it now assumes arectangular configuration. The purpose of the square or rectangular die31 is to impart sharp corners 33 to the twisted tape 30 so that whenplaced upon a mandrel 35 (FIG. 12A) in a heated state under pressure,the likelihood of entrapping air within the composite is minimized.Small amounts of trapped air or voids decrease strength, shear strength,fatigue life and band element durability. However, if desired, twistedtape 30 could be wrapped about a mandrel to form a band layer withoutfirst being pultrated into a rectangular configuration.

Referring to FIG. 12, in this sectional view looking along the length orlongitudinal direction of the twisted tape 30, the fibers 28 now spiraland cross over the neutral axis 35 of the individual twisted tape 30.This now leads to the preferred embodiment of the composite multilayertape band 10 depicted in FIGS. 13 and 14. Here a plurality of outsidelayers 37 and inside layers 38 of the band consists of strips ofconventional tapes 26 wound in layers with or without angularorientation as described in detail in said pending application Ser. No.08/782,364. The middle or central layer 40 near neutral axis 20 of theband 10 consists of tape made of twisted, pultrated fibers as shown inFIG. 11. As explained earlier, the maximum interlaminar shear stressoccurs along neutral axis 20 as the band deflects in the centralfootprint region and 45° ahead and behind the footprint region.

Now in the preferred embodiment, the neutral axis 20 of the bandbenefits by having many layers of twisted fibers 28 run across theneutral axis and assume a much larger role in resisting interlaminarshear. FIG. 15, which is an axial or end view of the preferredembodiment of band 10, further illustrates the effect near neutral axis20 of the twisted, pultrated tapes 30 and how the fibers 28 clearlycross the neutral axis. Also, the first interface 42 between the centralcore 40 of the twisted layer and either the inside layers 38 or outsidelayers 37 is well removed from neutral axis 20. The amount of twist perunit length can vary depending upon the desired dimensions of the tape,but the preferred amount of twist would achieve approximately a 45°angle relative to the longitudinal axis of the tape.

As shown in FIGS. 13 through 15, the preferred embodiment of themultilayer tape composite band consists of the following dimensionalranges: axial Width “w” determined by the tire size; thickness “t”determined by the thickness necessary for band element durability;thickness of the twisted tape layer equal to approx. ½ the band elementthickness; thickness of the inside layers and outer layers equal toapproximately ¼ the band element thickness; angle of twisted tapeapproximately 45° relative to the longitudinal axis of the tape.

In partial summary, a preferred embodiment has been disclosed for themultilayer tape composite band 10 which provides for multiple layers offibers 28 to cross neutral axis 20 of the band and enhance interlaminarshear strength. Also, there are now fewer interfaces 42 between thelayers, and they have been moved a comfortable distance away from theneutral axis 20 owing to the thickness of the central twisted layer 40.Consequently, the fatigue strength and durability of the band elementwill be correspondingly improved.

The concept of twisting tapes as shown in FIG. 9 is not restricted tosingle tapes. FIG. 16 depicts the concept of twisting two tapes 26 andhow the cross section can be altered. Once the twisted tapes have beenpassed through a suitable die for providing sharp corners, such as shownin FIG. 11, it can be placed upon the mandrel in conventional manner asshown in FIG. 12A. Obviously, the concept can be extended to three tapesand beyond. FIGS. 17 and 18 illustrate how two layers of tape 26 and 26Acombine to make up each twisted tape and the resulting band 45consisting of a central layer 46 formed of the double twisted tapes ofFIG. 16 with outer and inner conventional layers 47 and 48,respectively, of composite tapes. The heavier lines in FIG. 18 show theorientation of tape 26A combined with the lighter lines of tape 26.

FIGS. 19 and 20 depict another band embodiment 53 and method fororienting conventional composite thermoplastic tape layers formed fromstrips of tapes 26 so that fibers 28 are running across the neutral axis20 of the band. The construction of band 53 is achieved by winding tape26 on a mandrel to provide a plurality of convolutions which are builtup to form one monolithic thermoplastic band element. Inside layers 54and outside layers 55 are placed according to prior art wherein thestrips or tape 26 is placed about the mandrel in a direction generallyparallel to the surface of the mandrel, while the central layer 56 isformed by winding tape 26 at an angle, such as 45°, relative to axis 20,whereby one of the longitudinal edges 58 of the tape convolutions abutagainst inner layers 54 which was previously formed on the mandrel andthe opposite longitudinal edges 59 of the tape then providing thesupport for outer layers 55.

One method to form intermediate layer 56 would be to use a guide blockextending about one end of the mandrel with a surface angled ofapproximately 45° against which the flat surfaces of the individualconvolutions of tape 26 would be laid up against until sufficient layersor convolutions are wound about the mandrel to achieve the desired axiallength of the band. It is readily seen that with this arrangement, theindividual fibers 28 in the tape extend across neutral axis 20 toachieve the desired results. Again, the areas most susceptible tointerlaminar sheer will be where edges 58 and 59 join with inner andouter layers 54 and 55, which areas are considerable distances fromneutral axis 20.

FIGS. 21 and 22 depict still another band embodiment indicated generallyat 60, for providing fibers 28 that cross the neutral axis 20 of theband to achieve the benefits discussed earlier. Band 60 is a multilayertape composite band element consisting of a plurality of tape strips 26wound about a mandrel in a manner such as shown in pending patentapplication Ser. No. 08/782,346 forming a plurality of layers, eachseparated by a boundary 62. Impressions 61 or dimples are made in thelayers as they are deposited on the fabrication mandrel, such as with aroller die. The die makes the dimples in the layers such thatsubsequently applied layers fill in the depressions and thus provide acoupling or interfacial mechanical connection between the boundaries ofadjacent layers. The pattern of dimples or projections can be placedrandomly with high density and provide a significant improvement ininterlaminar shear strength both within and between layers of the bandelement. The individual fibers in the dimple areas also extend acrossneutral axis 20 and across the plane or boundary 62 between adjacenttape layers where the interlaminar sheer is most likely to occur.

The above embodiments are for multilayer tape composite band elements.However, the present invention is also applicable to homogeneousfilament wound bands. Homogeneous bands constructed of solid metal suchas aluminum or steel are outside the scope of this invention. However,homogeneous composite bands able to benefit from this preferred twistedfiber approach is the filament wound band 65 illustrated in FIGS. 25 and26. The cross section of a prior art filament wound composite band 65shows a uniform distribution of fibers 66 embedded in a resin matrix 67.There are no distinct layers in this configuration, the composite band65 is built up sequentially by filament winding one strand of smalldiameter fibers 66 upon another. This process is continued until thedesired cross section is accumulated, and is applicable for eitherthermoplastic or thermosetting material. As described and shown in FIGS.23 and 24, the band durability is limited by transverse shear failureoriginating near the neutral axis 20. Obviously, interlaminar shearfailure is applicable in this case because of the fiber orientation.

However, modification of this prior art filament band constructionaccording to the present invention, is the replacement of the centralportion of the filament wound band 65 with a layer 69 of the twisted,pultrated tape as described previously. As shown in FIGS. 25 and 26, thebenefit of this construction is to provide many fibers 28 running acrossthe neutral axis 20 which utilizes the strength of the fibers to augmentthe resin matrix in resisting transverse shear, increasing fatigue lifeand improving band durability. Inner and outer layers 63 and 64,respectively, formed of the wound filament fibers 66 are provided aboutintermediate layer 69 which assists in achieving the benefits of boththe filament fiber formed band and the twisted fiber reduction ofinterlaminar sheer.

It is readily understood that intermediate layer 69 can be formedaccording to the disclosure of FIG. 16 wherein two or more strips oftape 26 are placed in juxtaposition before being twisted and pultrated.

Another embodiment addresses both of the causes of composite bandelement failure. Recognizing that multilayer tape composite bandelements fail due to excessive shear either within layers or betweenlayers, band 70, shown in FIGS. 27 and 28 illustrates an arrangementwhich addresses both of these issues simultaneously. The band element 70is formed from a single layer of the twisted pultrated tape as shown inFIGS. 11 and 12A without any inner or outer layers being appliedthereto. It also can be formed as disclosed in FIG. 16 wherein aplurality of strips of tape 26 are placed in juxtaposition before beingtwisted. As discussed above, the twisted tape layer, such as indicatedat 40, 46 and 69 in FIGS. 13-14, 17-18 and 25-26 greatly enhances shearstrength owing to the fiber arrangement crossing the neutral axis 20 ofthe bands. Furthermore, the only interface between twisted tapes now isoriented in a plane 72 normal to the axis of the band. However, plane 72is not subjected to high levels of shear stress. Now the followingdesirable situation exists: The interface between twisted layers doesn'talign with the high shear stress plane. Thus, the interlaminar shearstrength of the resin at this interface is better able to provideadequate fatigue life and band element durability; The shear strengthwithin the twisted tapes is enhanced by the fiber orientation asexplained above.

In summary, preferred embodiments have been disclosed for multilayertape composite bands and homogeneous filament wound bands which providesfor multiple layers of fibers which cross the neutral axis of the bandelement and enhance interlaminar shear strength. Also, the number ofinterfaces between the layers has been reduced or eliminated, dependingon the embodiment chosen. Consequently, the fatigue strength anddurability of the band will be correspondingly improved.

Accordingly, the improved lightweight annular band for a pneumatic tireis simplified, provides an effective, safe, inexpensive, and efficientdevice which achieves all the enumerated objectives, provides foreliminating difficulties encountered with prior devices, and solvesproblems and obtains new results in the art.

In the foregoing description, certain terms have been used for brevity,clearness and understanding; but no unnecessary limitations are to beimplied therefrom beyond the requirement of the prior art, because suchterms are used for descriptive purpose and are intended to be broadlyconstrued.

Moreover, the description and illustration of the invention is by way ofexample, and the scope of the invention is not limited to the exactdetails shown or described.

Having now described the features, discoveries and principles of theinvention, the manner in which the improved band for a pneumatic tire isconstructed and used, the characteristics of the construction, and theadvantageous, new and useful results obtained, the new and usefulstructures, devices, elements, arrangements, parts, combinations andmethod steps, are set forth in the appended claims.

What is claimed is:
 1. A method of forming a thin annular band forembedding in a crown portion of a pneumatic tire including the steps of:A) providing a thin flat strip of material formed with a plurality oflongitudinally extending fibers embedded in a resin matrix; B) twistingthe strip until the strip assumes a substantially circular cross sectionthroughout its length; C) pultruting the twisted strip through a die toprovide the strip with a substantially rectangular cross section; D)wrapping the pultruted strip about a mandrel to form the band having aplurality of adjacent convolutions of said pultruted twisted strip; andE) forming inner and outer layers about the band by wrapping a firsthomogenous filament about the mandrel before wrapping the pultrutedtwisted strip thereon then wrapping a second homogenous filament overthe band formed from the pultruted twisted strip layer.
 2. The methoddefined in claim 1 including the step of placing a plurality of the thinstrips of material in elongated juxtaposition prior to twisting thestrip in step (B).